A company that awards points to its salespeople for making a sale and then allows those points to be exchanged for vacation packages is using ________ to modify sales behavior

The key take-home message from the author's discussion of crop circles is that

A) aliens or some form of extraterrestrial being has been trying to communicate with humans for hundreds of years. B) the cause of some real-world events are unexplainable and unknowable. C) critical thinkers must select the simpler of two claims that fit with the available evidence. D) hoaxters often impede scientific progress into the understanding of unexplainable events like the English crop circles.

Comparison groups are used to

a) Reduce threats to internal validity and construct validity b) Confirm rival hypotheses c) Rule out treatment effects d) Reduce threats to construct validity and external validity